Object sensing apparatus

ABSTRACT

An object sensing apparatus includes a plurality of light emitting diodes for illuminating a region of space and a plurality of closely arranged light detectors for receiving light reflected from an object. The apparatus is particularly useful in connection with automatically operated doors.

BACKGROUND OF THE INVENTION

This application is a divisional of prior application Ser. No. 347793,filed on Feb. 11, 1982, which was a continuation-in-part of pendingpatent application Ser. No. 155,008, filed May 30, 1980 now abandoned.

The present invention relates to an appartus for sensing the presence ofobjects within a selected region of space. In particular the presentinvention relates to object sensing devices which are useful inconnection with the operation of automatic doors or other automaticallymoving equipment.

In accordance with the prior art, it has been known to make use of lightor radiation emitting equipment and radiation detecting equipment forthe purpose of sensing the presence of an object or person in aparticular region of space. One application for such object sensingequipment is in connection with the operation of an automaticallyoperated door. In this case it is desirable to arrange the equipment tosense the approach of a person or an object, such as a shopping cart,from one direction of the door in order to activate the door to move itto the open position. It is likewise desirable to sense the presence ofan object or person on the opposite side of the door to prevent the doorfrom striking the person during the opening operation. Another sensingfunction is to determine when the person has passed through the doorway,and clear of the swing of the door, to enable closing of the door afterthe person has entered through the doorway.

The most reliable prior-art method for sensing the presence of a personis to provide pressure sensitive doormats which provide a signal inresponse to the weight of a person standing thereon. Such doormats mustbe provided on both sides of the door. On the approach side the doormatsenses the presence of a person who wishes to pass through the doorway.On the inside of the door, in the area which includes the swing path ofthe door, the mat is provided to sense the presence of a person orobject in the path of the door and provides a signal which prevents thedoor from opening and causing injury to the person or damage to theobject thereon. The inside swing path doormat is also used to preventclosing of the door during the time when a person is passing through thedoorway. After there is no weight on either of the doormats, the door ispermitted to close.

The use of pressure sensitive doormats in connection with the operationof a swinging door in accordance with the prior art, while being themost reliable known method for detecting the presence of a person orobject, has a disadvantage, which is normally associated with the use ofa doormat installation on a high traffic floor. The doormats used tosense the presence of a person or object are subject to wear from thepassage of traffic thereover. In addition, the doormats are usually inan outdoor entry location where they will be subjected to rainwater andto damage from ice, snow, and possibly salt or other corrosive chemicalsused to clear ice and snow.

A further problem with the doormat sensing devices is the fact that itbecomes difficult to tell when the device has failed. Failure of theswing path doormat can result in injury to a person and consequentliability to the owner or occupant of the premises in which the door hasbeen installed.

There have also been provided object sensing devices wherein a radiationsource is provided which sends radiation along a selected path toward aradiation sensing element. When an object or person enters the path ofthe radiation, the absence of the radiation being received at thesensing element provides an indication that there is an object or personin the path of the beam. The use of the beam-path type sensor provides acertain "fail safe" reliability because of the fact that a beam mustpass completely through the path in order to be detected and provide anindication of a safe condition. It becomes necessary, however, inconnection with the operation of a swinging door, to provide a greatmany emitters and detectors to provide adequate assurance that a smallchild is not within the path of the swinging door.

U.S. Pat. No. 3,852,592 to Scoville describes a prior art door openingcontrol apparatus which includes an emitter mounted above the doorwaywhich sends infrared radiation along a downwardly directed energy beamwhich spans a path of travel of pedestrian traffic approaching thedoorway. There is provided a sensing element which is mounted on the jamof the doorway and which has a receiving beam pattern of sensitivitywhich is generally horizontally disposed, so that there is provided anintersection of the infrared radiation beam from the emitter and thehorizontal sensing beam pattern from the receiver, which defines aprotected area in space. The patent states that additional emitters maybe provided, as requried, to provide additional protection in additionalregions in space.

While the apparatus described by Scoville may be effective in ordinarycircumstances for detecting objects which are in the region defined bythe intersection of the two beams, problems may arise from the fact thatthe door swings into the region of intersection of the two beams, andthe door may interfere with operation of the system. In addition, thesystem may be sensitive to its installation, since the emitter and thedetector are located at different locations, and the operation of thesedevices is sensitive to their locations and to their environment.Further, the system may fail to detect small objects, for example aninfant crawling below the horizontal beam.

It is therefore an object of the present invention to provide a new andimproved object detecting apparatus.

It is a further object of the present invention to provide such anapparatus which has a single location for emitters and detectors.

It is a further object of the present invention to provide such anapparatus which is less sensitive to the environment of itsinstallation, and is less sensitive to changes in the reflectivity ofthe object to be detected.

SUMMARY OF THE INVENTION

In accordance with the invention there is provided an apparatus forsensing objects which includes a plurality of radiation emittingelements each arranged to radiate a diverging beam of radiation into aselected region of space from a position on one side of the region ofspace. There is also provided a plurality of radiation sensing elements,arranged in proximity to the emitting elements for receiving radiationreflected from a radiation reflecting object within the region.

In a preferred arrangement the transmitting and receiving elemnts arearranged along separate straight lines which are separated by a smalldistance, for example, less than 16 mm. The transmitting and receivingelements are preferably arranged with equal spacing along respectivestraight lines and interspersed with each other. The distance betweenadjacent transmitting and receiving elements is preferably less than 20mm.

In another arrangement according to the invention there are providedfirst and second arrays of transmitting elements arranged on oppositesides of an array of receiving elements. The transmitting arrays radiateinto overlapping regions of space, and the receiving array receivesradiation from both regions.

In one embodiment the transmitting and receiving elements are arrangedin adjoining channels having opaque U-shaped cross sections. Thechannels provide a limitation on the radiation and receiving angles ofthe emitters and receivers to limit their transmitted and received beamsto a selected region of space within which it is desired to detectobjects.

In accordance with the invention there is also provided a controlapparatus for an automatic door which has a motor operated means forswinging the door open in a selected first direction path from a doorframe in response to the approach of an object from a second direction,and for inhibiting operation of the motor operating means in response tothe presence of an object in the first direction path of the door. Thecontrol apparatus includes first and second object sensing apparatusmounted on the door and facing respectively in the first and seconddirections from the door. The first and second sensing apparatus eachconsisits of a plurality of transmitting elements for emitting adiverging beam of radiation in response to supplied electrical signals,and means for simultaneously supplying electrical signals to all of theelements in each sensing apparatus. Each sensing apparatus also includesa plurality of radiation detecting elements for receiving radiationreflected from an object, and a receiver connected to the detectingelements for providing an output signal representative of the presenceof an object. The apparatus also includes a control circuit for (1)activating the motor means to open the door in response to an outputsignal from the second sensing apparatus, (2) activating the motor meansto maintain the door in an open position in response to an output signalfrom the second sensing apparatus and (3) inhibiting operation of themotor means and preventing opening of the door in response to an outputsignal from the first sensing apparatus.

The control apparatus can be arranged so that the control circuit is notoperative to inhibit opening of the door after the motor means isoperated and the door is opened by a selected amount. This prevents thepresence of a railing or a wall adjacent the door opening frompreventing further opening of the door. There may also be provided aradiation emitting means arranged to direct radiation along a path tothe detecting elements of the first sensing apparatus when the door isopened. The control means is then arranged to activate the emittingmeans after the door is opened by a selected amount, and the controlmeans is arranged to inhibit operation of the motor means uponobstruction of the path between the emitting means and the detectingelements of the first sensing apparatus.

Another aspect of the invention is the provision of a receiver for anobject detecting system for a door operator which provides reducedreceiver sensitivity upon the initiation of door operation.

In accordance with another aspect of the invention, there is provided anobject detecting system wherein a series of pulses of radiation areemitted and wherein radiation reflected from objects is detected duringthe emission, thereby to detect the presence of an object. The apparatusis an arrangement for preventing interference from radiation emitted bya similar system. The apparatus includes a transmitter sequencing meanswhich periodically generates pulse signals to cause the system toradiate. The sequencing means is responsive to a control signal forinhibiting pulse generation. The apparatus further includes a receiverwhich provides an output signal indicating the detection of radiation.The output signal is supplied to the sequencing means as a controlsignal. Finally, the apparatus includes an output means which providesan object indicating signal only upon concurrance of the pulse signaland the output signal.

The sensing apparatus of the invention may also be used in connectionwith machine tools, automatic transport vehicles, elevator doors andsimilar equipment for preventing such equipment from striking an objector person.

For a better understanding of the present invention, together with otherand further objects, reference is made to the folloiwng description,taken in conjunction with the accompanying drawings, and its scope willbe pointed out in the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates the sensing apparatus of the present invention inschematic form.

FIG. 2 illustrates the sensing apparatus of the present invention asinstalled on an automatic operating door.

FIG. 3 is a top view of the door of FIG. 2.

FIG. 4 is a side view of the door of FIG. 2 illustrating the radiationand receiving pattern of the sensor assembly.

FIG. 5 is a top view of the FIG. 2 door illustrating the sensor assemblytransmitting and receiving pattern.

FIG. 6 is a cross-section view of a sensor assembly suitable for use inconnection with the door of FIG. 2.

FIG. 7 is a front view of the sensor assembly of FIG. 6.

FIG. 8 is a schematic diagram of the FIG. 6 sensor assembly.

FIG. 9 is a block diagram illustrating the arrangement of the controlapparatus usable for operating the door of FIG. 2.

FIG. 10 is a front view of another sensor assembly in accordance withthe invention.

FIG. 11 is a cross sectional view of the FIG. 10 sensor assembly.

FIG. 12 is a side view of a door having installed thereon the sensorassembly of FIG. 10 and illustrating the transmitting pattern of thesensor assembly.

FIG. 13 is a top view of a multiple door sensor installation.

FIG. 14 is a block diagram of an arrangement for preventing sensorassembly interference.

FIGS. 15A and 15B are graphs showing pulse sequences for the FIG. 14arrangement.

FIG. 16 is a block and schematic diagram illustrating an arrangement forsensitivity reduction.

DESCRIPTION OF THE INVENTION

In FIG. 1 there is shown a schematic diagram of the sensor assembly inaccordance with the present invention. In the FIG. 1, diagram the sensorassembly 10 includes a source 12 for generating electrical signals,preferably pulse signals having a predetermined frequency such as a fewkilohertz. The output of signal source 12 is provided to light-emittingdiodes, which are connected in series with signal source 12. Thoseskilled in the art will recognize that it will also be possible toconnect the light-emitting diodes 14 in parallel with the output ofsignal source 12, according to the voltage output of the signal sourceand the impedance of the diodes. Each of the light-emitting diodes 14 isarranged to radiate a diverging pattern of radiation. In the embodimentillustrated in FIG. 1 the light-emitting diodes 14 are each arranged toradiate in a conical pattern with an interior angle 18 which isapproximately equal to 90°. Accordingly, objects 22, 24 and 26, whichare within the radiation pattern of one or more of the light-emittingdiodes 14 will receive radiation such as optical or infrared radiation,which is emitted from the diodes.

The sensor assembly 10 of FIG. 1 also includes a plurality of radiationdetecting elements 16, such as photo-transistors. The photo-transistors16 are arragned to have a diverging beam of radiation sensitivity,approximately the same shape as the beam of the light-emitting diodes14. Accordingly, light or infrared radiation, emitted by light-emittingdiodes 14, and reflected from an object 22, 24 or 26 within the regionof space illuminated by the sensor assembly, will be reflected back intothe light detecting elements 16 and generate therein an electricalsignal. It should be noted that because of the diverging beams ofradiation of the light-emitting diodes 14 and the diverging beam ofsensitivity of the light-sensing elements 16, it will be possible forradiation, emitted by any of the diodes, to be reflected off an objectin the object field and received by a plurality of the light-sensitiveelements 16. This feature tends to increase the sensitivity of thesensing apparatus for relatively close objects, and thereby enables theeasy detection of objects in the adjoining region of space, even ifthose objects have varying amounts of radiation reflectivity at thefrequency of emission of the light sources 14.

The light sensing elements 16 are connected in parallel and their outputsignals are provided as in input to receiver 20. Receiver 20 preferablyincludes a tuned amplifier which is responsive to frequencies in therange of the output frequency of electrical signals from signal source12.

The detecting apparatus of FIG. 1 is particularly useful in connectionwith automatically operated mechanical equipment for sensing thepresence of an obstacle. In this respect, the sensing apparatus of FIG.1 is preferred to the conventional reflection type object sensingapparatus by reason of the fact that it is less susceptible tovariations in object detecting range with variation in radiationreflectivity of the object. Prior art reflection type object sensingapparatus makes use of a focused or collimated beam of light, which isdirected outward in the direction from which an object is anticipated toapproach. The radiation is reflected off the object and received by asensing apparatus which also has a relatively-narrow, focused beam whichis oriented in the identical direction. The range at which an objectwill be sensed by this type of apparatus will depend largely on thereflectivity of the object. An object such as a retro-reflecting device,which sends back a relatively focused beam of radiation toward theemitter will cause a very large response in the receiving device and maybe detected at a very large range. An object of irregular shape whichhas relatively low reflectivity, such as a dull black overcoat, will notbe detected until it is very close to the radiation detector.

Because the sensing apparatus illustrated in FIG. 1 uses a plurality ofoverlapping diverging light beams, forming diffuse light, rather thanfocused beams of radiation, for both the radiation emitting devices andthe radiation detecting devices, it is susceptible to receiving andresponding to radiation reflected off objects only within a limitedrange where multiple emitters illuminate the object with diffuse lightand multiple receivers detect the reflected diffuse light. Therefore,the radiation detector is not likely to respond to an object at arelatively far distance, even if that object is highly reflective, sinceboth the illumination of the object and the sensitivity of the detectorsis greatly reduced with distance because of the diffuse nature of theillumination and detection as compared to focused beam illumination anddetecting devices. In contrast, the sensing apparatus will respondrelatively strongly to an object which is relatively close, because eventhough the reflection from the object may be diffused and scattered, itwill be received by multiple detecting elements in the receiving array,and therefore, the output of these elements, as currents, will add inthe receiver, and provide an adequate response to provide an outputindication of the presence of the object.

FIG. 2 is a perspective view and FIG. 3 is a top, cross-sectional viewof an automatically operated door 30 having a sensing apparatus 10 inaccordance with the present invention. The door 30 is mounted withinwall 28 and is opened and closed by means of a motor apparatus 33. Oneach side of the door there are provided guard rails 34, 36, 38 and 40,which are arranged to prevent approach toward the door from directionsother than straight-on. The door of FIG. 2 is arranged to open in afirst direction which is away from the side illustrated in FIG. 2, andalong the path 31 to the position 30' which is illustrated in FIG. 3.Opening of the door 30 by motor 33 is effected in response to thedetection of an object by sensing apparatus 10, which is mounted on theside of the door illustrated in FIG. 2 facing in a second direction withrespect to the door. The door is provided with a second object sensingapparatus 15 which is mounted on the side of the door facing in thefirst direction corresponding to the door opening path. Sensingapparatus 15 is utilized by the door control apparatus to preventopening of the door when there is an obstruction in the path of thedoor, such as a person standing next to the door. The sensing apparatus15 inhibits the operation of the door when an object or person is sensedin its path in order to prevent damage to the door or injury to theperson.

The object sensing devices 10 and 15 which are mounted on the door 30are illustrated schematically in FIG. 1. FIGS. 4 and 5 illustraterespectively the elevation and azimuth radiation transmitting andreceiving beams for the sensing devices 10 and 15. The apparatus 10 hasa radiation surface which is angled at approximately 30° from thevertical in order to orient the elevation radiation beam in a slightlyupward from horizontal direction. The radiation beam has anapproximately 90° half power beam width so that it radiates into an area42 illustrated in elevation in FIG. 4 and in azimuth in FIG. 5. Thedevice 10 is mounted approximately 15" above the floor on door 30 todetect objects near the bottom of the door.

The radiation sensing apparatus 10 is illustrated in greater detail inFIGS. 6 and 7. The apparatus includes a pair of U-shaped channels 46,48, made of opaque material, such as extruded aluminum. The channelshave an outer surface which is cut off at the 30° angle illustrated inFIG. 4, and they are covered by a light transmitting cover 50,preferably have a tinting suitable to transmit and receive primarilyradiation in the frequency bank of operation of the light-emittingdiodes 14. The light-emitting diodes 14 are contained in the upperchannel 46. The photo-sensitive transistors 16 are contained in a lowerchannel 48. The location of the light-emitting diodes andphoto-sensitive transistors in each of the channels is such as toprovide the 90° radiation beam width which is illustrated in FIG. 4 andshown as dotted lines in FIG. 6. At the bottom of each of the channels46 and 48 of the extruded member 44, there are provided circuits 52 forconnecting the light emitting diodes and the photo transistors to thesignal generating and receiving apparatus.

In the front plan view of FIG. 7, the spacing of the elements of thesensor assembly 10 is illustrated in greater detail. In the preferredembodiment illustrated, the light-emitting diodes 14 are arranged withapproximately equal spacing along a first path which consists of ahorizontal straight line down the center of the upper channel 46. Thephoto transistors 16 are arranged with similar equal spacing,interspersed with the diodes 14, along another straight path, whichconsists of the center line of the lower channel 48. The spacing betweenadjacent photo transistors and light-emitting diodes, designated spacingA in FIG. 7, is preferably selected to be approximately 20 millimetersor less. The spacing B between the paths on which are located thelight-emitting diodes 14 and the photo transistors 16 is preferably nomore than 16 millimeters. Spacings A and B which are greater than therecommended amounts have been found to make it difficult to obtain aresponse from small objects, such as sticks the size of fingers, withinthe region of space 42 illustrated in FIGS. 4 and 5. With the suggestedspacing the device 10 will sense small objects out to a distance ofapproximately 5 to 8 feet. Naturally the range of the sensing apparatuscan be adjusted according to the intensity of the diodes 14 and thesensitivity of the detectors 16 and the receiver.

FIG. 8 is a circuit diagram illustrating the circuits for the sensingapparatus 10. As illustrated in FIG. 8 the light-emitting diodes areconnected in series to a signal source 12, and optically coupled to thephoto transistors by means of reflection off an object. Phototransistors 16 are connected in parallel to drive a tuned amplifier 54in the receiver 22. The output of the tuned amplifier is detected by arectifier 56 and provided to a DC amplifier 58 which can operate a relayor other decision logic used in connection with the operation of thedoor. FIG. 9 illustrates a block diagram of the control apparatus usablein connection with the door 30 of FIG. 2. The control unit, which may bea programmed microprocessor or equivalent logic circuits, is connectedto sensing apparatus 10, sensing apparatus 15 and also in a preferredembodiment there may be provided an additional light source 32 which isarranged on barrier 40 as illustrated in FIG. 3. The output of thecontrol unit is connected to motor 33 and is arranged to operate themotor to open and close the door 30.

The control circuit illustrated in FIG. 6 under normal conditionsoperates to open the door in response to an object detecting signalemitted by detecting apparatus 10. Detecting apparatus 15 operates toinhibit activation of door opening when an object obstructs the door.Accordingly control unit 54 will not open the door when a signal isreceived from unit 15, even if a signal is received from unit 10.

It will be recognized that as door 30 opens control unit 15 will respondto the presence of barrier 40 in the path of the door and provide anoutput indication to control unit 54 indicating that an object is in thepath of the door. This, under ordinary circumstances, would stop thefurther opening of the door. In order to prevent this false detection,the sensing unit 15 is inhibited by a signal from position switch 56which indicates that the door has opened to a certain selected angle,for example, position 39. Signals received from detecting apparatus 15indicating the presence of an object in the path of the door are nolonger operative to prevent the control unit from effecting thecontinued opening of the door after switch 56 is activated. Suchinactivation of the operation of sensing apparatus 15 may cause ahazardous condition because of the fact that, after the control unit isinhibited, a child can enter the path of the door and be injured by thedoor. In order to provide further safety under this circumstance,barrier 40 may be provided with light-emitting means 32 which emitslight in the direction of sensing apparatus 15 after the position switch56 is activated by opening of the door to position 39. Thereafter lightpasses directly from unit 32 to detecting apparatus 15, and causes anoutput signal from apparatus 15. At this point the output signal fromapparatus 15 is considered to be a positive signal, and the furtheropening of the door will be inhibited only upon the interruption of thelight path between unit 32 and detecting apparatus 15.

FIG. 10 shows an alternative arrangement for the transmitting andreceiving elements. The FIG. 10 sensor assembly 62 includes two lineararrays of transmitting elements 14, such as light emitting diodes, whichare arranged along straight lines on opposite sides of an array ofreceiving elements 16. As illustrated in the cross-sectional view ofFIG. 11, the transmitting and receiving arrays are located in channelsformed in the structural housing of the sensor assembly. The upper andlower transmitting channels containing elements 14 are inclined at anangle of approximately 20° above and below the beam direction of thereceiving elements 16. This arrangement for the transmitting elementsprovides better object illumination when used in connection with a door,as illustrated in FIG. 12. The sensor assembly 62 is shown in FIG. 12mounted near the vertical center of a door 30 and having a compositeradiation pattern 61 formed by the overlapping radiation from the upperand lower transmitting arrays of sensor assembly 62.

Those skilled in the art will recognize that it is likewise possible toachieve better radiation pattern coverage as illustrated in FIG. 12 byusing upper and lower inclined receiving arrays and a centraltransmitting element array.

FIG. 13 illustrates an installation wherein object detectors 10 and 10'of the type shown in FIG. 7 are mounted on doors 30 and 30', which faceeach other across a common entrance. As indicated by dotted arrow 64, itbecomes possible in this type of installation to have one sensorassembly emit radiation which is received by the other sensor assembly,either directly or through reflection. This transmission from one sensorto the other can cause interference in the normal operation of thesystems.

FIG. 14 is a block diagram of an arrangement whereby such interferencecan be avoided. The system shown in FIG. 14 is incorporated into theoperational electronics of each of the sensors shown in FIG. 13 andoperates independently so that the sensors need not be connectedtogether or otherwise coordinated in operation.

Each sensor assembly is provided with a sequencer 64 which providesperiodic pulses to the sensor transmitter 12 thereby causing thetransmitter to emit a pulse of modulated radiation, such as amplitudemodulated infrared radiation. The pulses from sensor 64 are repeated ata regular, selected time interval.

Sequencer 64 is responsive to a control signal, provided to the holdinput, which causes a delay in the output of a transmitter keying pulsefor the duration of the control signal. The output of the sensorreceiver 28 is connected to the sequencer as a control signal. Thus, ifa sequencer is providing a sequence of pulses as shown in FIG. 15A,having pulses 68, 70, etc., and the sensor assembly is within visiblerange of another sensor assembly having the pulse sequence shown in FIG.15B, with pulse 76, 78, 80, there comes a time when pulse 72 in FIG. 15Awould have interference from pulse 80 in FIG. 15B. According to thearrangement of FIG. 14, pulse 80 is received by receiver 20 and providesa hold control signal to sequencer 64 which delays the initiation ofpulse 72 to the position 72' so that there is no interference of pulses72 and 80. Sequencer 64 then continues its usual pulse sequences asshown by pulse 74.

In order to prevent receiver interference the output of receiver 20 iscombined with the sequencer output in an AND gate 66 for operation ofthe relay. Accordingly, for each sensor assembly, an object detectionsignal is provided only when a signal is received while the transmitterof that sensor assembly is operating. This prevents any interferencebetween a pair of sensor assemblies.

Those skilled in the art will recognize that the sequencer 64 and gate66 can be of conventional digital logic design. For example, thesequencer 64 can include a counter which provides periodic output pulsesin response to a certain count signal derived from a clock. The holdsignal can be used to gate the clock signal, and thereby delay a pulsewhen a signal is received by receiver 20.

FIG. 16 shows a further improvement in the present invention, which isuseful for the sensor assemblies which are installed as door openers andthe like. In connection with door opening, it is sometimes appropriateto reduce sensitivity of the sensor assemblies when the door isoperating, for example, to prevent detection of a wall toward which thedoor is swinging. The circuit of FIG. 14 is a modification of thereceiver 20 shown in FIG. 8 wherein a switch 84 is provided inconnection with resistors 82 and 86, to provide reduced signalsensitivity when the door opening relay 60 is operative.

While the preferred emboidments of the invention have been described inconnection with a motor operated swinging door, those skilled in the artwill recognize that this and other embodiments will be useful inconnection with sliding doors, elevator doors, self operated vehicles orother automatically moving devices.

While I have described what I believe to be the preferred embodiments ofthe invention, those skilled in the art will recognize that other andfurther changes and modifications may be made thereto, and it isintended to claim all such changes as fall within the true scope of theinvention.

I claim:
 1. Obstacle detection apparatus comprising:first and secondtransmitting arrays each having a plurality of radiation emittingelements spaced along a respective one of first and secondmutually-parallel, spaced-apart, straight lines, said elements in eacharray including radiation beamwidth controlling means for providing arespective one of first and second selected diverging radiationbeamwidths in an angular coordinate transverse to the line along whichthe elements are spaced, said elements of each array having a respectiveone of third and fourth wide radiation beamwidths in a plane includingthe line along which the elements are spaced, and said elements in eacharray having substantially the same beam direction, whereby the beams ofsaid elements of the array overlap in said plane to form diffusedillumination; a receiving array comprising a plurality of radiationdetecting elements spaced along a third straight line, parallel to andspaced from said first and second straight lines, said elementsincluding beamwidth controlling means for providing a selected divergingfirst receiving beamwidth in an angular coordinate transverse to saidthird line, said detecting elements having a wide second receivingbeamwidth in a plane including said third line, each of said detectingelements having substantially the same direction of sensitivity wherebythe beams of said elements overlap and said elements collectivelyrespond to diffuse radiation; means for simultaneously providing saidemitter with electrical signals to be radiated; and means for receivingsignals detected by said detecting elements thereby to determine thepresence of a radiation reflecting object within a region of spacecorresponding to said first and second transmitting and said firstreceiving beamwidths and the length of said arrays.
 2. Apparatus asspecified in claim 1 wherein said first and second straight lines arearranged with equal spacing on opposite sides of said third straightline.
 3. Apparatus as specified in claim 1 wherein the beam directionsof said first and second transmitting array elements are at oppositeangles with respect to said direction of sensitivity.
 4. In an objectdetection system wherein a series of pulses of radiation are emitted andwherein radiation reflected from objects is detected during saidemission thereby to detect presence of an object, apparatus for avoidinginterference from radiation emitted from a similar systemcomprising:transmitter sequencing means for periodically generatingpulse signals to cause said emission of radiation, said sequencing meansbeing responsive to a control signal for inhibiting said pulsegeneration; a receiver providing an output signal indicating detectionof radiation, said output signal being supplied to said sequencing meansas a control signal; and output means, responsive to said pulse signalsand said output signal, for providing an object indicating signal onlyupon concurrence of said pulse signal and said output signal.